1. Technical Field
The invention relates to mechanical jarring devices for use in drilling. Jarring devices are employed, for example, to loosen or release objects or obstructions in a bore-hole, such as a drill bit which has become jammed.
2. Description of Prior Art
U.S. Pat. specification No. 1,798,480 describes jarring devices of this type. Such devices include members which are connected together for limited relative longitudinal movement. The members are held together by means which provide for a sudden release of the members for longitudinal movement causing a jarring or hammering action.
The prior specification referred to describes a jarring device in which the two members are held in a retracted position by latch means which can be released by simple reciprocation of one of the members. This avoids relatively complex arrangements hitherto employed such as the use of pressurised fluids or rotation of the drill string to which the jarring device is attached.
This simple method of operation is achieved by the provision of a latching device comprising a sliding sleeve which can slide relative to one of the members and which is connected to the member by axial tension springs. The sliding sleeve carries a plurality of pivoted latching elements which can engage with a cooperating abutment on the other of the members to prevent relative movement between the members. The latching elements are held in position by a locking collar associated with said one of the members.
The latching means is released by applying pressure to the other of the members causing an increase in tension in the tension springs to a predetermined value when the latching means is released. When this occurs, the members can move relative to one another under the action of the tension springs causing a sudden jarring or hammering effect.
An object of the present invention is to provide an improved jarring device which is simple to operate and which is robust, reliable in use, and has low wear characteristics.
A further object is to provide a jarring device in which the jarring impacts are directed in both longitudinal directions.